Hello, in this introduction, I want to first introduce you to some basic terminology. Hopefully, this will be the only slide in the whole series that has this many words, but these are important words because these concepts are going to be things that carry you through the entire series. So, let's start at the top. Central nervous system, that's your brain and spinal cord, and those are the parts of your nervous system that are entirely encased in bone. Nucleus is a group of neurons within the central nervous system with a similar function, connectivity, and neurotransmitters. You'll see that word nucleus, if you ever take a course in cell biology, and it's a term that talks about the part of the cell that contains DNA and we'll talk about that a little bit when we talk about neurons, but the bottom line is a nucleus in the nervous system, is a group of neurons with similar function. Tract, that's a bundle of axons that are traveling together within the CNS, and this is usually, a bunch of axons that are going from one place to another together, connecting two parts of the nervous system. We'll talk about some specific tracts, as we move through the course. Synapse, that's a point of communication between two neurons or neurons and their target organs like muscle or glands, and it's part of the electro-chemical transmission, that is the basic pattern of communication between cells, in the nervous system. Afferent, means arriving. Note the alliteration two 'a's, arriving information. It can be looked at as a cell information coming to and from, arriving at a particular neuron or information arriving at a whole group of neurons. Efferent is exiting information. This is information that exits a neuron, exits a nucleus or exits the CNS. The peripheral nervous system is all of the stuff that's not inside the bones. So, those are your cranial nerves, that come out to innervate structures and targets in your head and neck, and your peripheral nerves or spinal nerves that come out of your spinal cord and go to all of your muscles, and a nerve, it's similar to a tract except this time, it's outside the CNS. So, a nerve is a bundle of axons, with their associated connective tissue elements for support and blood vessels, located outside the brain and spinal cord. Ganglia, that's a group of neurons outside the CNS that has similar function, connectivity, and neurotransmitters. I don't know why we have to have separate words for within and without and outside the CNS but we do. So, ganglia are outside, a nucleus is inside. The somatic nervous system is all of the afferent and efferent systems that regulate the motor innervation of your skeletal muscles, and the sensory information from your external environment. When we're talking about the somatics, we're talking about the part of the nervous system of which you're aware. So you know where the mosquito bit you, you're able to dance and jump up and down, those are all voluntary or very finely localized sensations. So that's our somatic nervous system. Our autonomic nervous system, in contrast, is again going to contain afferent and efferent systems, but they regulate smooth muscle and glands, and they are the sensory apparatus of your internal environment. So all of the things that move around, on the inside like your intestines, your blood vessels, smooth muscles that control the pupil. All of those things, are in the autonomic nervous system. The directional flow of information is one of the most important concepts you can grasp, when you're learning about the nervous system. Afferent is arriving information, efferent is exiting information. So, if we use, if we look at these little diagram. So, if we have neuron A, it is sending afferent information is coming in, from out here and it's efferent information is exiting through its axon, down to neuron B. So, neuron B has arriving information from neuron A, and then it's exiting information, goes to neuron C. If we have a group of neurons, functioning together as we defined in our terminology and nucleus, we have nucleus A, it's exiting information is going to nucleus B, so nucleus B, has afferent information from A, and then efferent information is going to C. So this is the basic way, the basic plan of the flow of information, afferent arrives, efferent exits. Another way to look at this, is afferent is often talked about as sensory information, because sensory information is arriving from all your entire surrounding, everything you hear, see, and feel, is arriving information into through your body, and into your CNS. Motor information is always referred to as exiting or efferent information because it's the desire to move, is generated within the CNS and then moves out of the CNS along your nerves to your muscles, so that you can actually realize that motion, that you were thinking about. Neurons, this is my favorite little drawing, I made. This is neurons are like other cells in the body, they have a cell body, they have a nucleus, where its DNA is kept. Neurons are a little special though, because they have these extensions of the cell body. So these little guys here, on the sides are dendrites. Dendrites are the receptive fields of the neuron, and they are where information is coming in. So, information is arriving via the dendrites to the cell body. Neurons do two, well, one thing, well two things, they fire or they don't fire, fire, don't fire. So, they're kind of binary that way. If they're going to fire, that exiting information, goes along their axon, travels all the way down here and then, interacts with another cell or a target organ like a muscle or smooth muscle cell, through these little terminal buttons or synapses. Okay. So, neurons are really complicated, very highly, they're kind of the prima donnas of cell of the body, in that they only do the one thing, they make neurotransmitters, they receive information and then based on summing up that information, to fire or not fire, they send it down the axon to a synapse. Gray matter and white matter, gray matter and white matter are two words that describe the appearance, the gross anatomical appearance of the central nervous system when it's sectioned. So, in the brain, which is over here, we have the gray matter on the outside, it's a little bit darker and you'll see this in subsequent imagery, as we get into the other lectures, and then, the gray matter is made up of neuronal cell bodies and their proximal dendrites. Deep to the gray matter, is the white matter and these are all the fiber tracts, that we'll be talking about in later segments, and it's made up of myelinated axons. The reason it's white, is because myelin is highly enriched in lipids and the lipids in a fresh appearance look white. In the spinal cord, we have just the opposite, we have the white matter on the outside, and the gray matter on the inside. So, in the spinal cord are neurons and proximal dendrites are all hidden here in this gray butterfly and our white matter fiber tracts, are all around the outside. So, in summary, I really want you to concentrate on your terminology, because that's going to carry you through the rest of the lectures. Remember and always remember, afferent versus efferent, afferent arrives, efferent exits, and remember gray matter versus white matter, what's in the gray matter, and what's in the white matter, and why are they a little bit different. That concludes this segment.